Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 176)

Publication 1747-UM010B-EN-P - September 2003
A-12 Specifications
BT throughput is always slower than discrete data transfer.
Completing a BT is dependent on the time involved for the:
•
SLC control program to enable the BT via an M0 file write
(1)
•
backup scanner to detect that a BT has been requested
(2)
•
BT to be waiting in the queue due to another BT already being
processed on the same logical rack
(3)
•
backup scanner to schedule a pending bit
(2)
•
adapter to acknowledge the request
(4)
•
backup scanner to initiate the BT and transfer the data
(2)
•
SLC control program to detect that the BT has completed
(DN flag set)
(1)
The time to free up the BT buffer (by clearing the EN flag so another
BT can be performed) depends on the:
•
BT instruction time when the rung transitions from true to false,
which clears the EN flag
(5)
•
time for the backup scanner to detect that the EN flag has been
cleared
(6)
•
BT instruction time to detect that the DN flag has been cleared
(5)
The formula to calculate BT throughput is:
T
M0 +
T
SNo-bt
(number of BTs + 1) + T
btwait +
2T
RIO +
2T
btx +
T
adp-bt +
T
ps
The equation for freeing up the BT buffer is:
T
M0 +
TS
No-bt
(number of BTs) + T
ps
(1) This is dependent on the SLC processor you are using.
(2) Refer to the equations that follow.
(3) The RIO network allows only one BT per logical rack (not logical device) per RIO scan. Therefore, if multiple BTs
are performed on devices within the same logical rack, BTs have to wait in the queue until any previously
scheduled BTs for the same logical rack are completed.
(4) This is dependent on the RIO adapter.
(5) This is dependent on the SLC processor you are using.
(6) Refer to the equations that follow.